Quick Revision Notes

Class 11 Biology: Structural Organisation in Animals

MP Board Curriculum

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Introduction

• Tissue (ऊतक): A group of similar cells along with intercellular substances performing a specific function.
• Organ (अंग): Tissues are organized in specific proportions and patterns to form an organ (e.g., stomach, lung).
• Organ System (अंग तंत्र): Two or more organs interact physically or chemically to form an organ system (e.g., digestive system).

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1. Animal Tissues (जंतु ऊतक)

Animal tissues are broadly classified into four types based on their structure and function:

1. Epithelial Tissue (उपला ऊतक)
2. Connective Tissue (संयोजी ऊतक)
3. Muscular Tissue (पेशीय ऊतक)
4. Neural Tissue (तंत्रिका ऊतक)

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2. Epithelial Tissue (उपकला ऊतक)

• Characteristics: Free surface facing body fluid or outside environment; cells compactly packed with little intercellular matrix.
• Types:
  • Simple Epithelium (सरल उपकला): Single layer of cells; functions as a lining for body cavities, ducts, and tubes.
    • Squamous (शल्ककी): Thin, flat, tile-like (e.g., walls of blood vessels, air sacs of lungs).
    • Cuboidal (घनाकार): Cube-like cells; secretion and absorption (e.g., ducts of glands, nephrons).
    • Columnar (स्तंभाकार): Tall, slender cells; nuclei at the base; absorption and secretion (e.g., lining of stomach and intestine).
    • Ciliated (पक्ष्माभी): Columnar or cuboidal cells with cilia on their free surface; move particles in a specific direction (e.g., bronchioles, fallopian tubes).
  • Compound Epithelium (संयुक्त उपकला): Multi-layered; protective function against chemical and mechanical stresses (e.g., dry surface of skin, moist surface of buccal cavity).
• Glands (ग्रंथियाँ):
  • Unicellular: Goblet cells of the alimentary canal.
  • Multicellular: Salivary glands.
  • Exocrine: Release secretions (mucus, saliva, earwax, oil, milk, digestive enzymes) via ducts.
  • Endocrine: Ductless; release hormones directly into the fluid bathing the gland.

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3. Connective Tissue (संयोजी ऊतक)

• Characteristics: Most abundant and widely distributed in complex animals; links and supports other tissues/organs.
• Components: Cells secrete structural proteins called collagen or elastin (except blood), which provide strength, elasticity, and flexibility, embedded in a modified polysaccharide matrix.
• Types:
  1. Loose Connective Tissue (ढीला संयोजी ऊतक):
     • Areolar Tissue: Present beneath the skin; supports epithelium. Contains fibroblasts, macrophages, and mast cells.
     • Adipose Tissue: Located mainly beneath skin; stores fats; acts as a fat reservoir and thermal insulator.
  2. Dense Connective Tissue (सघन संयोजी ऊतक): Fibers and fibroblasts are compactly packed.
     • Dense regular: Tendons (attach skeletal muscles to bones) and ligaments (attach bone to bone).
     • Dense irregular: Present in skin; has fibroblasts and fibers oriented differently.
  3. Specialized Connective Tissue (विशेष संयोजी ऊतक):
     • Cartilage (उपास्थि): Solid, pliable matrix resisting compression (e.g., tip of nose, outer ear joints, between vertebrate bones).
     • Bone (अस्थि): Hard, non-pliable matrix rich in calcium salts and collagen; gives structural frame; supports soft tissues (e.g., long bones). Contains bone cells (osteocytes) in spaces called lacunae.
     • Blood (रक्त): Fluid connective tissue containing plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets; circulates transport substances.

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4. Muscular Tissue (पेशीय ऊतक)

• Composed of long, cylindrical fibers arranged in parallel arrays. Made of fine fibrils called myofibrils.
• Types:
  1. Skeletal Muscle (कंकाल पेशी): Closely attached to skeletal bones; striated (striped); voluntary in action.
  2. Smooth Muscle (चिकनी पेशी): Spindle-shaped; non-striated; involuntary (e.g., walls of internal organs like blood vessels, stomach, intestine).
  3. Cardiac Muscle (हृदय पेशी): Contractile tissue present only in the heart; striated; involuntary; cells communicate via intercalated discs.

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5. Neural Tissue (तंत्रिका ऊतक)

• Exerts the greatest control over the body's responsiveness to changing conditions.
• Consists of Neurons (excitable cells) and Neuroglial cells (protect and support neurons).
• Neuron Parts: Cyton (cell body), dendrites (short, branched projections), and axon (long, fiber carrying impulses away from the cell body).

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6. Organ and Organ System

• Cells $\rightarrow$ Tissues $\rightarrow$ Organs $\rightarrow$ Organ Systems $\rightarrow$ Organism.
• This hierarchical organization ensures division of labor and efficient functioning of the multicellular body.

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7. Morphology and Anatomy of Animals (Case Studies)

A. Cockroach (Periplaneta americana) - Insecta, Arthropoda

• Scientific Name: Periplaneta americana
• Body Divisions: Head, Thorax, and Abdomen.
• Exoskeleton: Hard chitinous, brown/black colored. Each segment has hardened plates called sclerites (tergites dorsally, sternites ventrally).
• Digestive System: Foregut, Midgut (has hepatic caeca for digestive juice secretion), and Hindgut. Malpighian tubules help in excretion.
• Blood Vascular System: Open type; haemolymph flows in a fluid-filled cavity (haemocoel). Heart is 13-chambered.
• Respiration: Network of trachea opening through 10 pairs of small holes called spiracles.
• Nervous System: Series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side.
• Reproductive System: Dioecious (separate sexes). Both males and females have well-developed reproductive organs. Females produce 9-10 oothecae (capsules containing fertilized eggs).
• Development: Paurometabolous (development through nymphal stages resembling adults via moulting).

B. Earthworm (Pheretima posthuma) - Annelida

• Body Division: Metamerically segmented body (100–120 segments).
• Dorsal/Ventral surface: Dorsal surface is marked by a median dark line (dorsal blood vessel); ventral has genital openings.
• Clitellum: Segments 14–16 are thickened and glandular, forming a prominent band called clitellum (used in cocoon formation).
• Digestive System: Straight tube from segment 1 to the last. Includes pharynx, esophagus, stomach, intestine (features typhlosole from segment 26 to 95 to increase absorptive surface area).
• Circulatory System: Closed type; consists of blood vessels, capillaries, and lateral hearts (lateral hearts in 4th & 6th segments, lateral-oesophageal in 7th & 9th segments). Blood contains hemoglobin dissolved in plasma.
• Excretion: Excretory organs are segmentally arranged coiled tubes called nephridia (Septal, Pharyngeal, and Integumentary).
• Reproductive System: Hermaphrodite (bisexually monoecious). Contains both testes and ovaries. Cross-fertilization occurs via cocoons.

C. Frog (Rana tigrina) - Amphibia, Chordata

• Skin: Smooth, slippery, moist, maintained by mucous glands (helps in cutaneous respiration). Coloration is olive-green with dark spots on dorsal side.
• Body Divisions: Head and Trunk (Neck and tail are absent).
• Digestive System: Complete digestive tract. Digestion takes place in stomach and intestine. Liver secretes bile stored in the gall bladder.
• Respiration:
  • In Water: Cutaneous respiration (diffusion through skin).
  • On Land: Buccal cavity, skin, and lungs (pulmonary respiration).
• Circulatory System: Closed, lymphatic system present. 3-chambered heart (two atria and one ventricle). Sinus venosus and truncus arteriosus are present. RBCs are nucleated.
• Excretory System: Pair of kidneys (mesonephric). Frogs are ureotelic animals (excrete urea).
• Nervous System: Central (brain and spinal cord), Peripheral (cranial and spinal nerves), and Autonomous nervous system. Brain enclosed in a bony brain box (cranium).
• Reproductive System: Separate sexes. Fertilization is external; takes place in water. Development involves a larval stage called tadpole.